The present invention relates to linear drives, particularly linear drives like ones used in machine tools as a feed unit. For example, what are known as parallel kinematic machine tools are equipped with such feed units in their telescopic arms.
For example, WO 99/42245 A1 discloses a linear drive including a housing and a rail at which the housing is mounted for relative movement of the housing along the rail. In particular, this linear drive is provided with a carrier and a carrier housing, on which the carrier is mounted such that it can be moved longitudinally. Drive elements are provided on the carrier and on the carrier housing to produce relative movement between the carrier and the carrier housing. The carrier has a double T cross-sectional profile. The drive elements are primary and secondary parts in the form of coils or magnets to allow a direct electric drive. These linear drives are preferably used as feed axes in parallel structures. When used as a feed unit in machine tools, but also in other applications, high accelerations and retardations of the linear drive are desired in order to reach a desired actuating position quickly and reliably. The feed produced by the linear drive then has to be completed when a desired actuating position has been reached. In known linear drives, proper positioning, therefore also including braking, can be performed via the drive elements. In the event of power failure, positioning can no longer be carried out.